Flexible thermosetting acrylic coating compositions

ABSTRACT

The thermosetting acrylic enamel has as film-forming constituents A POLYBLEND OF A RELATIVELY HARD ACRYLIC POLYMER THAT HAS A GLASS TRANSITION TEMPERATURE OF GREATER THAN -20*C., and a soft acrylic polymer that has a glass transition temperature of less than -20*C., wherein the difference in glass transition temperature between the hard and soft acrylic polymer is at least 30*C.; and A HEAT REACTIVE CONDENSATE SUCH AS HEXA-(METHOXYMETHYL)MELAMINE, A BUTYLATED OR METHYLATED MELAMINE FORMALDEHYDE RESIN, OR A POLYISOCYANATE THAT IS COMPATIBLE WITH THE POLYBLEND; THE ACRYLIC ENAMEL FORMS A FLEXIBLE, DURABLE FINISH USEFUL FOR EXAMPLE FOR RUBBER-COATED AUTOMOBILE AND TRUCK BUMPERS, AS A FINISH FOR PLASTICS FOR FOAMED STRUCTURES, FOR FLEXIBLE METAL SUBSTRATES, FOR EXAMPLE, FOR COIL COATINGS

United States Patent 1 Victorius FLEXIBLE THERMOSETTING ACRYLIC COATING COMPOSITIONS [75] Inventor: Claus Victorius, Media, Pa.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

221 Filed: May 26, 1972 [21] Appl. No.: 257,239

[52] U.S. Cl...... 260/41 B, 260/31.2 R, 260/33.6 U, 260/41 C, 260/856, 260/859, 117/61 1511 Int. Cl C08g 39/10, C08g 51/22 [58] Field of Search 260/901, 856, 859, 260/41 BC, 334 R, 33.6 U, 328 R, 31.2 R; 117/161 [56] References Cited UNITED STATES PATENTS 3,249,463 6/1966 Carlee .L 117/76 3,028,367 4/1962 OBrien..... 260/77.5 3,438,800 4/1969 Johnson.... 117/64. 3,557,033 l/197l Briton 260/21 OTHER PUBLICATIONS I Film-Forming Compositions, Allyn Acrylic Ester Resins, pp. 38-68, 1967,

hexa(methoxymethyl )melamine,- a

[ Nov. 20, 1973 Primary ExaminerAllan Lieberman Assistant ExaminerRichard Zaitlen Attorney-Hilmar L. Fricke [5 7 ABSTRACT The thermosetting acrylic enamel has as film-forming constituents D a polyblend of a relatively hardv acrylic polymer that has a glass transition temperature of greater than 20C., and a soft acrylic polymer that has a glass transition temperature of less than 20C.,

wherein the difference in glass transition temperature between the hard and soft acrylic polymer is at least 8 Claims, No Drawings FLEXIBLE THERMOSETTING ACRYLIC COATING COMPOSITIONS BACKGROUND OF THE INVENTION This invention relates to a thermosetting acrylic enamel and in particular to a thermosetting acrylic enamel that forms a tough, flexible and durable finish.

Thermosetting acrylic enamels are known as shown in Frazier et al. U.S. Pat. No. 2,681,897, issued June 22, 1954, Bearden U.S. Pat. No. 3,311,583, issued Mar. 28, 1967', Vasta U.S. Pat. No. 3,338,860, issued Aug. 29, 1967; Fisk et al. U.S. Pat. No. 3,365,414, issued Jan. 23, 1968; Vasta U.S. Pat. No. 3,622,651, issued Nov. 23, 1971. These coating compositions are adequate for many usesv but do nothave the balance of properties necessary for flexible finishes for. rubbercoated automobile and truck bumpers, for foamed mcntioned properties.

STATEMENT OF THE INVENTION The liquid coating composition comprises -50'percent by weight of film-forming constituents and a solvent for these constituents; wherein the film-forming constituents comprise:

1. 70-95 percent by weight, based on the weight of the film-forming constituents, of a polyblend of A. 60-95 percent by weight, based on the weight of the polyblend, of a relatively hard acrylic polymer that has a glass transition temperature of greater than -20C. and consists essentially of l. 20-60 percent by weight, based on the weight of the acrylic polymer, of an alkyl methacrylate having one to four carbon atoms in the alkyl group or styrene or a mixture of the alkyl methacrylate and styrene;

2. 20-75 percent by weight, based on the weight of the acrylic polymer, of an alkyl methacrylate having 6 to 12 carbon atoms in the alkyl group or an alkyl acrylate having two to twelve carbon atoms in the alkyl group or a mixture of these constituents;

3. 5-20 percent by weight, based on the weight of the acrylic polymer, ofa hydroxy alkyl acrylate or a hydroxy alkyl methacrylate or a mixture of these constituents having two to four carbon atoms in the alkyl groups;

B. 5-40 percent by weight, based on the weight of the polyblend, of a soft acrylic polymer having a glass transition temperature of less than -20C. and consisting essentially of 1. 80-95 percent by weight, based on the weight of the acrylic polymer, of an alkyl acrylate having two to twelve carbon atoms in the alkyl group or an alkyl methacrylate having eight to twelve carbon atoms in the alkyl group or a mixture of these constituents; and

2. 5-20 percent by weight, based on the weight rylate or a hydroxy alkyl methacrylate or a DESCRIPTION OF THE INVENTION I The novel coating composition of this invention has a solids content of film-forming constituents of about 10-50 percent'and preferably, about 20-40 percent by weight. The novel composition can be clear or pigmented and if pigmented contains about 01-20 percent by weight pigmentj The film-forming constituents used in the novel coating composition comprise -95 percent by weight of.

a polyblend and correspondingly 30-5 percent by weight of a compatible crosslinking agent. The polyblend contains 60-95 percent by weight of a relatively hard acrylic polymer that has a' glass transition tempertime of r ter than-29 wab w iG-ans! 49-,5 percent by weight of a soft acrylic polymer which has a glass transition temperature of about 20C to about 80C., provided that the difference in glass transition temperature between the hard and soft acrylic polymer is at least 30C., and preferably about 35C. to 70C.

The acrylic polymers utilized in this invention are prepared by conventional polymerization techniques in which thefrnonomers are blended with solvents and polymerization catalysts and heated-to about -150C. for about 2-6 hours to form a polymer that has a relative viscosity of about 1.05-1.30 and preferably, about 1.06-1.20.

The relative viscosity is the value obtained by dividing the efflux time of the solution of the polymer by the efflux time of the solvent used to form the above polymer solution. The efflux times are measured according to the procedure of ASTM-D-445-46-T, Method B, using as the polymer solution 0.5 gram of the polymer dissolved in methlethyl ketone to give 50 cubic centimeters of solution. The efflux time is measured at a temperature of 30C. in a standard apparatus sold underthe designation of modified Ostwald viscometer.

Typical solvents which are used to prepare the acrylic polymer-and also used as diluent in the novel coating composition of this invention are toluene, xylene, butyl acetate, ethyl acetate, acetone, methlethyl ketone, methyl-isobutyl ketone, ethyl alcohol, butyl alcohol and other aromatic hydrocarbons, cycloaliphatic hydrocarbons, esters, ethers, ketones and alcohols, such as are conventionally used.

About 0.1-4 percent by weight, based on the weight of the monomers used to prepare the acrylic polymer, of a polymerization catalyst, is used. Typical catalysts are azo-bis-isobutyronitrile, azo-bis-(a, gammadimethyl-valeronitrile), benzoyl peroxide, t-butylperoxy pivalate, di-tert-butyl peroxide and the like. Up to 5 percent by weight of a chain transfer agent can be used to control molecular weight such as dodecyl mercaptan or benzene thiol.

The glass transition temperature of the acrylic polymer is the temperature at which the viscosity of the polymer is poises.

The combination of a hard and soft acrylic polymer for a particular polyblend enamel composition is usually chosen so that the two polymers contain the same alkyl acrylate or alkyl methacrylate or both.

The hard acrylic polymer utilized in the novel coating composition of this invention contains -60 percent by weight, based on the acrylic polymer, of an alkyl methacrylate that has one to four carbons in the alkyl group or styrene or a mixture of the alkyl methacrylate and styrene. Typical alkyl methacrylates which can be used are methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate and the like. Preferably, the hard acrylic polymer contains 24.9-55 percent by weight of methyl methacrylate.

The hard acrylic polymer also contains 20-75 percent by weight, based on the weight of the acrylic polymer, of an alkyl methacrylate that has six to twelve carbon atoms in the alkyl group, or an alkyl acrylate that has two to twelve carbon atoms in the alkyl group or a mixture of the alkyl methacrylate and the alkyl acrylate. Typical alkyl methacrylates that can be used are hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, and lauryl methacrylate. Typical alkyl acrylates that can be used are ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl-acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate and the like. Preferably the hard acrylic polymer contains 35-60 percent by weight of an alkyl acrylate having two to eight carbon atoms in the alkyl group.

The hard acrylic polymer contains 5-20 percent by weight, preferably 5-15 percent by weight of hydroxy alkyl acrylate or a hydroxy alkyl methacrylate or a mixture thereof that has two to four carbon atoms in the alkyl groups. Typical compounds of this type are hydroxyethyl acrylate, hydroxypropylacrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate and the like.

The soft acrylic polymer contains 80-95 percent by weight of an alkyl acrylate that has two to twelve carbon atoms in the alkyl group or an alkyl methacrylate that has eight to twelve carbon atoms in the alkyl group or a mixture of these constituents. Any of the aforementioned alkyl acrylates and alkyl methacrylates can be utilized in preparing this soft acrylic polymer. Correspondingly, the soft acrylic polymer contains 5-20 percent by weight ofa hydroxy alkyl acrylate or a hydroxy alkyl methacrylate that has two to four carbon atoms in the alkyl group. Any of the aforementioned hydroxy alkyl methacrylates or acrylates can be used in preparing the soft acrylic polymer.

The soft acrylic polymer can contain up to 20 percent by weight of an alkyl methacrylate having one to four carbon atoms in the alkyl group or styrene provided that the glass' transition temperature is below -20C.

Both the hard and the soft acrylic polymer can contain 0.1-5 percent by weight of an a,B-ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, ethacrylic acid, propyl carylic acid, and the like.

One preferred soft acrylic polymer contains 85-94.9 percent by weight of an alkyl acrylate having two to eight carbon atoms in the alkyl group, 5-15 percent by weight of a hydroxy alkyl acrylate or methacrylate having two to four carbon atoms in the alkyl group and 0.1-5 percent by weight of methacrylic acid or acrylic acid.

One highly preferred soft acrylic polymer contains 85-95 percent by weight of ethyl acrylate and 5-l5 percent by weight of hydroxyethyl acrylate and has a glass transition temperature 22C. to -23C.

Another highly preferred soft acrylic polymer contains 80-94 percent by weight of butyl acrylate, 5-15 percent by weight of hydroxy ethylacrylate and 1-5 percent by weight of acrylic or methacrylic acid and has a glass transition temperature of about 44C. to about 5 2C. I

The following are preferred hard acrylic polymers:

28-50 percent by weight of methyl methacrylate, 40-46 percent by weight of butyl acrylate, 5-15 percent by weight of hydroxyethyl acrylate, 1-5 percent by weight of acrylic acid or methacrylic acid wherein the polymer has a glass transition temperature of about 16C to -l9C; and

35-55 percent by weight of methyl methacrylate, 30-60 percent by weight of ethyl acrylate and 5-15 percent by weight of hydroxy ethyl acrylate having a glass transition temperature of about 34C to 10C.

The cross-linking agent used in the novel coating composition of this invention is compatible with both the acrylic polymers of the polyblend and can either be an alkylolated melamine formaldehyde resin or a polyisocyanate. Typical alkylolated melamine formaldehyde resins have one to eight carbon atoms in the alkyl group and are resins that are well known in the art. These resins are prepared by conventional techniques in which a lower alkyl alcohol such as methanol, ethanol, butanol, isobutanol, propanol, isopropanol hexanol, 2-ethyl hexanol and the like is reacted with a melamine formaldehyde to provide pendent alkoxy groups.

Preferred melamine resins that are used in this invention are butylated melamine formaldehyde resins, methylated/butylated melamine formaldehyde resins and hexa-(methoxymethyl) melamine.

An acid catalyst can be used in the novel composition such as para-toluene sulfonic acid or butyl acid phosphate. An acid catalyst is needed if there is an absence of acid groups in the acrylic polymer or if a low temperature cure is required, or if a highly etherified melamine resin is used such as hexa(methoxymethyl)melamine.

A variety of organic polyisocyanates can be used in the novel coating composition of this invention and include aliphatic, cycloaliphatic, aralkyl, heterocyclic and aryl polyisocyanates. Typical polyisocyantes are, for example, toluene-2,4-diisocyanate, diphenyl methane-4,4'-diisocyanate, methylene-bis-(4- 'cyclohexylisocyanate), tetramethylene diisocyanate,

toluene diisocyanate and trimethylol propane. These polyisocyanates can be made according to Bunge et al. U. SfPat. No. 2,855,421, issued Oct. 7, 1958. I

Polyisocyanates of a biuret, for example, the biuret of hexamethylene diisocyanate made according to Mayer et al. US. Pat. No. 3,245,941, issued Apr. 12, 1966, can also be used.

Organic plasticizers can also be used in the novel coating composition of this invention in amounts up to l-lO percent by weight based on the weight of filmforming constituents. Monomeric and polymeric plasticizers can be used such as phthalate ester plasticizers, and in particular, alkyl and cycloalkyl ester phthlates in which the alkyl groups have two to ten carbon atoms such as dioctyl phthalate, didecyl phthalate, butyl benzylphthalate, dicyclohexyl phthalate and mixtures thereof. Epoxidized soya bean oil, oil free and oil modified alkyds can also be used as plasticizers. Polyester resins such as alkylene glycol esters of adipic and benzoic acid, for example, ethylene glycol adipate benzoate,-neopentyl glycol adipate benzoate, ethylene glycol adipate benzoate phthalate, can also be used in the novel coating composition of this invention.

The novel coating composition of this invention can be pigmented. Typical pigments which can be used are metallic oxides, preferably titanium dioxide, zinc oxide, iron oxide, and the like, metallic flakes, such as aluminum flake, metallic powders, metallic hydroxides, Afflair pigments, i.e., mica coated with titanium dioxide, sulfates, carbonates, carbon blacks, silica, talc, china clay and other pigments, organic dyes and lakes.

Other compatible resins can be incorporated into the novel coating composition of this invention such as vinyl chloride copolymers, polyurethanes, cellulose acetate butyrate, and silicone resins.

The novel coating composition of this invention is applied to a dry substrate such as polyurethane, a foamed polyurethane, rubber, fiberglass, plastic, metal, rubber or foam coated metal by any of the usual application methods, such as spraying electrostatic spraying, dipping, brushing flowcoating and the like. These coatings are then baked for about 5-40 minutes at about 80-200C. Shorter baking times can be used such as 1 minute at about 250C. if the composition is applied by a high-speed coating line. The resulting coating is about 0.5-5 mils thick, preferably a coating of about l-3 mils in thickness is used. Room temperature curing is also possible with an acid catalyst.

The resulting dried and cured coating is a polyblend structure in which the hard acrylic polymer surrounds particles of the soft acrylic polymer and the entire both phases and forms a uniformly cross-linked struc- V Example 1 Polymer A solution is prepared as follows:

Parts By Weight. Methyl methacrylate monomer 40.0 Z-Hydroxyethyl acrylatemonomer 10.0 Butyl acrylate monomer 50.0 Methylethyl ketone l00.0 Azo-bisisobutyronitrile l.2 Total 20l.2

The above ingredients are charged into a vessel which is immersed in a water bath maintained at C. and the vessel is tumbled in this water bath for a period of 16 hours. The resulting solution is clear and homogeneous and does not contain gel particles. 50 Parts by weight of ethylene glycol monoethylether acetate are added to provide a polymer solution having a solids content of 39.7 percent. The resulting hard polymer has a calculated glass transition temperature of 7C.

, Polymer B solution is prepared as follows:

Parts By Weight Z-Hydroxethyl arcylate 10.0 Butyl acrylate monomer 90.0 Methylethyl ketone 100.0 Azo-bisisobutyronitrile 0.6 Total 200.6

' The above ingredients are charged into a vessel which is placed in a water bath maintained at.70C. and tumbled for 16 hours. The resulting polymer solution is cleared and does not contain gel particles. 50 Parts by weight of ethylene glycol' monoethylether acetate are added to the polymersolution to form a solution having a 38.9 percent solids content. The resulting soft polymer has a calculated glass transition temperature of 52C.

A coating composition is prepared as follows:

Parts By Weight Polymer A solution (prepared above) 30.2 Polymer B solutiontprepared above) 7.7 "Cyme| 301 hexa(methoxymethyl) melamine l.2

A 2% solution of para-toluene sulfonic acid in isopropanol l.2 Solvent blend (methylethyl ketone/ethylene glycol monoethylether acetate in a l/l ratio) 4.7 5.0

Total 4 The above ingredients are thoroughly blended together to form a coating composition.

The coating composition is reduced to a spray viscosity with conventional'solvents and applied to astyrene butadiene rubber-coated metal substrate, a polyurethane foam utilized in automobile interiors, and a polyurethane foam utilized for automotive bumpers and 7 baked for.30 minutes at 120C. The resulting coating has excellent adhesion to the substrate, good flexibility, good toughness and had a good appearance and is not hazy in color. Films formed from the novel coating composition have a high elongation at break.

EXAMPLE 2 Polymer C solution is prepared as follows:

Parts by Weight Butyl acrylate monomer 400.0 Methyl methacrylate monomer 296.0 Z-Hydroxy ethyl acrylate 80.0 Acrylic acid 24.0 Methylethyl ketone 800.0 Dodecyl mercaptan 4.0 Azo-bisisobutyronitrile 8.0 Total 1,612.0

The above ingredients are charged into a reaction vessel which is immersed in a water bath maintained at 70C. and the vessel is tumbled in the water bath for 16 hours. The resulting polymer solution is clear and homogeneous and does not contain gel particles. The polymer solution has a polymer solids content of 47.9 percent and the resulting hard polymer has a relative viscosity of 1.102 and a calculated glass transition temperature 7C.

Polymer D solution is prepared as follows:

Parts By Weight Butyl acrylate 87.0 Z-Hydroxy ethyl acrylate 10.0 Acrylic Acid 3.0 Methyl ethyl ketone 100.0 Azo-bisisobutyronitrile 1.0 Total 201.0

The above ingredients are charged into a reaction vessel which is immersed in a water bath maintained at 70C. and the vessel is tumbled in the water bath for 16 hours. The resulting polymer solution isclear and hoinogeneous and does not contain gel particles. 50 Parts by weight of ethylene glycol mono-ethyl ether acetate are added to give a polymer solution having a 35.4 percent polymer solids content. The resulting soft polymer has a relative viscosity of 1.151 and a calculated glass transition temperature of 49C.

A coating composition is prepared as follows:

Parts By Weight Polymer C solution (prepared above) 20.5

Polymer D solution (prepared above) 11.9 liutylatcd melamine formaldehyde resin solution (555% resin solids in butanol) 4.0

Ethylene glycol monoethyl ether acetate 8.7

Total 45.1

Parts By Weight Polymer C solution (prepared above) 265.3 Polymer D solution (prepared above) 145.3 Butylated Melamine Formaldehyde Resin solution (described above) 62.1 Mill Base (titanium dioxide pigment dispersed in a copolymer of styrene/butylacrylate/Z-hydroxy ethylacrylate/acrylic acid having a pigment to hinder ratio of 413/ and a total solids content of 78.3%) 158.7 Total 631.4

The above ingredients are thoroughly blended together to form an enamel composition. This enamel is reduced to a 22 percent solids content with a solvent of methylethyl ketone/toluene in a 1/1 weight ratio. The resulting enamel is sprayed onto the following substrates:

1. Soft, self-skinned flexible urethane foam;

2. Steel coated with about 30 mils of urethane rubber.

The coating is allowed to dry for about 15 minutes and'then is baked for 30 minutes at C. The result- 7 ing finish is about 2 mils thick and is smooth and has a high gloss (20 gloss of about.70). The finish is tough, flexible and non-tacky at room temperature. The finish on the urethane foam does not crack at -35C and when indented to a depth of of an inch with a 74 inch steel ball. The finish on the urethane rubber coated steel does not crack whensubjected to 80 inch-pound bump at 25C.

EXAMPLES 3-11 In each of the Examples, a hard copolymer and a soft copolymer are prepared using a procedure very similar to procedure as shown in Example 2, except different monomer constituents are utiliied' as shown in the Table. 1n each case, the glass transition temperature of the hard and soft copolymer are calculated. The coating composition then is preparedby blending the hard and soft copolymer in the ratio shown with a cross-linking agent. 0.2 percent by weight of para toluene sulfonic acid catalyst is added to Examples 6-8. The resulting coating composition is applied as in Example 2 to a polyurethane foam and baked as shown in the Table. A clear film is formed from each of the coating compositions, then the properties of the films are measured and recorded in the attached Table.

EXAMPLE 12 A coating composition is prepared as follows:

1.7 Total 34.5

The above ingredients are thoroughly blended together to form a coating composition.

The coating composition is reduced to a spray viscosity with conventional solvents and applied to a rubber TABLE coated bumper and to a polyurethane foam substrate and the coating is allowed to air dry for 30 minutes and then baked for 30 minutes at 125C. The resulting finish is clear-tough and flexible.

5 A clear film is formed from the coating composition and has the following physical properties:

30 percent elongation at break Tukon Hardness of 2.3

Flexible and tough.

The invention claimed is:

l. A thermosetting acrylic coating composition comprising 10-50 percent by weight of film-forming constituents and a solvent for these constituents; wherein the film-forming constituents comprise:

1. 70-95 percent by weight, based on the weight of the film-forming constituents, of a polyblend of A. 60-95 percent by weight, based on the weight of the polyblend, of a relatively hard acrylic polyrner having a glass transition temperature greater than -20C. to 40C. and consisting essentially of 1. 20-60 percent by weight based on'the weight of the acrylic polymer, of methyl methacrylate or styrene or a mixture thereof; 2. 20-75 percent by weight, based on the weight of the acrylic polymer, of an alkyl acrylate having two to twelve carbon atoms in the alkyl group or a mixture thereof; 3. 5-20 percent by.weight, based on the weight of the acrylic polymer, of a hydroxy alkyl acrylate or a hydroxy alkyl methacrylate or a mixture thereof having two to four carbon atoms in the alkyl groups; B. 5-40 percent by weight, based on the weight of the polyblend of a soft acrylic polymer having a glass transition temperature of less than 20C., to -80C. and consisting essentially of 1. 80-95 percent by weight, based on the weight of the acrylic polymer, of an alkyl acrylate having two to twelve carbon atoms in the alkyl 40 group; and

2. 5-20 percent by weight, based on the weight of the acrylic polymer, of a hydroxyl alkyl acry- Ratio acrylic resin cross- Bake linking temperaagent ture, C. Properties of finish nnd film 100/16 30 X120 Flexible, tough and strong, 20% elongation creaseable at 35 C. 1 100/16 30' X 120 Excellent properties. 100/16 30 X 120 Excellent flexibility and toughness. 100/16 30 X 120 Excellent properties. 100/8 30 X 120 Very flexible and tough; creaseable. 85/15 30 X 150 Hard, flexible and tough. 90/10 1 X 275 Hard, flexible, tough. 20% elongation before break, creaseable. 100/12 30 X 130 Yen flexible and tough. 100/16 30 120 Excellent physical properties. 100/16 30 X 120 Very tough, flexible, 20% elongation at break. 2-Ethylhexyl acrylate, HEA=2-Hydroxyethyl acrylate, AA=Acrylie acid, MAA= Ratio hard to soft copolynier Cross-linking agent 70/30 Butylated MF 70/30 do 70/30 (1o.. s 70/30 do 1 0/10 Hexa(methoxymethyl) melamine. 80/20 do 70/30 do 0/10 Methylatedl but ated MF. 00/10 Butylated MF. 80/20 ..do

2-EHA:

=Bntyl acrylate.

=Ethyl acrylate, BA

ture thereof having 2 to 4 carbon atoms in the alkyl groups;

wherein the difference in glass transistion temperature between hard and soft acrylic polymer is 35 to 70C., and the hardand soft acrylic polymers have a relative viscosity of about 1.05-1.30.

11. 5-30 percent by weight, based on the weight of the film forming constituents, of a heat reactive alkylated melamine formaldehyde having one to eight carbon atoms in the alkyl group or a polyisocyanate.

R V Soft. copolymci 1.102 BA/HEA/AA (87/10/31). 1.102 BA/HEA/AA (90/713). 1.102 2-EHA/MMA/HEA/AA (/12/1013). 1.144 2-EHA/HEA/AA (87/10/3). .19 BA/HEA I 27 EA/HEA (90/10). 1.081 EAIHEA (/5). 1.175 BA/HEA/MMA v (87/10/3). 1.114 RA/HEA/AA (87/10/3). 1. 090 BA/HEA/AA (87/10/3).

=Butylmethaery1ate, EA Relative viscosity.

Glass transition temperature,

yl methacrylate, BMA

hard acrylic polymer consists essentially of 1. 24.9-55 percent by weight of methyl methacrylate, 2. 35-60 percent of an alkyl acrylate having two to eight carbon atoms in the alkyl group,

3. 5-15 percent by weight of a hydroxy alkyl acrylate or a hydroxy alkyl methacrylate having two to four carbon atoms in the alkyl group,

4. 0.1-5 percent by weight of methacrylic acid or acrylic acid;

the soft polymer consists essentially of 1. 85-949 percent by weight of an alkyl arcylate having 2-8 carbon atoms in the alkyl group;

2. 5-15 percent by weight of a h droxy alkyl acrylate /M.\lA/1lEA/AA (50/37/10/3) MMA n'EA/AA 10/3). BA/MMA/HEA EA/MAA MA/gEA/AA B'A s nEA AA (50/37/10/3). I Styrene, MMA=Meth Methacrylic acid, MF formaldehyde resin, R.V.

(50/35/15). 8 MMA/EA/IIEA (50/40/10). BA/MMA/ ll (60/27/10/3).

=1v1elarnint:

Example llaid (opolymt r 2 BA/MMA/llEA/AA 3 5 BA/ 6 7 MMA/EA/HEA late or a hydroxyl alkyl methacrylate or a mix- 2. The coating composition of claim I in which the I 1 1 or a hydroxy alkyl methyacrylate having 2 to 4 carbon atoms in the alkyl groups, and

3. 01-5 percent by weight of methacrylic acid or acrylic acid. 3. The coating composition of claim 1 in which the hard polymer consists essentially of 28-50 percent by weight of methyl methacrylate, 40-46 percent by weight of butyl acrylate,

5-l 5 percent by weight of hydroxy ethyl acrylate and hard acrylic polymer consists essentially of 35-55 percent of weight of methyl methacrylate, 30-60 percent by weight of ethyl arcylate, 5-l5 percent by weight of hydroxyethyl acrylate, having a glass transition temperature of about 34C to 10C;

the soft acrylic polymer consists essentially of -95 percent by weight of ethyl acrylate, 5-15 percent by weight of hydroxyethyl acrylate, that has a glass transition temperature of -22C. to about --23C.

5. The coating composition of claim 4 in which the heat reactive condensate consists essentially of hexa(- methoxymethyl) melamine.

6. The coating composition of claim 4 in which the heat reactive condensate consists essentially of the biuret of hexamethylene diisocyanate.

7. The coating composition of claim 1 containing 0.l20 percent by weight of pigment.

8. A substrate having a dried coalesced coating of the composition of claim 1 which is a cross-linked, twophase structure having the soft acrylic polymer dispersed in the hard acrylic polymer and providing substantially clear film. 

2. 5-20 percent by weight, based on the weight of the acrylic polymer, of a hydroxyl alkyl acrylate or a hydroxyl alkyl methacrylate or a mixture thereof having 2 to 4 carbon atoms in the alkyl groups; wherein the difference in glass transistion temperature between hard and soft acrylic polymer is 35* to 70*C., and the hard and soft acrylic polymers have a relative viscosity of about 1.05-1.30. II. 5-30 percent by weight, based on the weight of the film forming constituents, of a heat reactive alkylated melamine formaldehyde having one to eight carbon atoms in the alkyl group or a polyisocyanate.
 2. The coating composition of claim 1 in which the hard acrylic polymer consists essentially of
 2. 35-60 percent of an alkyl acrylate having two to eight carbon atoms in the alkyl group,
 2. 20-75 percent by weight, based on the weight of the acrylic polymer, of an alkyl acrylate having two to twelve carbon atoms in the alkyl group or a mixture thereof;
 2. 5-15 percent by weight of a hydroxy alkyl acrylate or a hydroxy alkyl methyacrylate having 2 to 4 carbon atoms in the alkyl groups, and
 3. 0.1-5 percent by weight of methacrylic acid or acrylic acid.
 3. 5-20 percent by weight, based on the weight of the acrylic polymer, of a hydroxy alkyl acrylate or a hydroxy alkyl methacrylate or a mixture thereof having two to four carbon atoms in the alkyl groups; B. 5-40 percent by weight, based on the weight of the polyblend of a soft acrylic polymer having a glass transition temperature of less than -20*C., to -80*C. and consisting essentially of
 3. 5-15 percent by weight of a hydroxy alkyl acrylate or a hydroxy alkyl methacrylate having two to four carbon atoms in the alkyl group,
 3. The coating composition of claim 1 in which the hard polymer consists essentially of 28-50 percent by weight of methyl methacrylate, 40-46 percent by weight of butyl acrylate, 5-15 percent by weight of hydroxy ethyl acrylate and 1-5 percent by weight of acrylic acid or methacrylic acid and has a glass transition temperature of about 16*C to -19*C.; and the soft polymer consists essentially of 80-90 percent by weight of butyl acrylate, 5-15 percent by weight of hydroxy ethyl acrylate, 1-5 percent by weight of acrylic acid or methacrylic acid and has a glass transition temperature of about -44*C. to -52*C.; and the heat reactive condensate is a butylated melamine formaldehyde resin or hexa(methoxymethyl) melamine.
 4. The coating composition of claim 1 in which the hard acrylic polymer consists essentially of 35-55 percent of weight of methyl methacrylate, 30-60 percent by weight of ethyl arcylate, 5-15 percent by weight of hydroxyethyl acrylate, having a glass transition temperature of about 34*C to 10*C; the soft acrylic polymer consists essentially of 85-95 percent by weight of ethyl acrylate, 5-15 percent by weight of hydroxyethyl acrylate, that has a glass transition temperature of -22*C. to about -23*C.
 4. 0.1-5 percent by weight of methacrylic acid or acrylic acid; the soft polymer consists essentially of
 5. The coating composition of claim 4 in which the heat reactive condensate consists essentially of hexa(methoxymethyl) melamine.
 6. The coating composition of claim 4 in which the heat reactive condensate consists essentially of the biuret of hexamethylene diisocyanate.
 7. The coating composition of claim 1 containing 0.1-20 percent by weight of pigment.
 8. A substrate having a dried coalesced coating of the composition of claim 1 which is a cross-linked, two-phase structure having the soft acrylic polymer dispersed in the hard acrylic polymer and providing substantially clear film. 